Variable thermal resistance mounting system

ABSTRACT

A variable-thermal-resistance mounting system may include a cylinder coupled to a heat source, or heat load and a rod movably engaged to the cylinder and coupled to a remaining one of the heat source and heat load. The rod may be coupled to a heat load. The rod may be axially slidable relative to the cylinder between a collapsed position and an extended position in a manner causing a change in heat flow between the heat source and the heat load such that the warm-side temperature of the heat load is initially set at a substantially optimal value.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to pending U.S. Provisional Application No. 61/728,233 filed on Nov. 19, 2013, and entitled VARIABLE THERMAL RESISTANCE MOUNTING SYSTEM, the entire contents of which is expressly incorporated herein by reference.

FIELD

The present disclosure relates generally to mounting systems for thermal platforms and, more particularly, to systems for optimizing heat flow to a heat load such as a thermoelectric generator.

BACKGROUND

Thermoelectric energy harvesting systems such as thermoelectric generators convert thermal energy into electrical energy in response to a thermal gradient across the thermoelectric generator. The thermal gradient may occur as a result of heat flow from a heat source that is thermally coupled to one side of the thermoelectric generator to a heat sink that is thermally coupled to the other side of the thermoelectric generator. The thermoelectric generator may have an optimal temperature or an optimal temperature range within which the thermoelectric generator operates at maximum efficiency. The thermoelectric generator may be coupled to electronic components for conditioning the voltage produced by the thermoelectric generator prior to delivery to a device (e.g., a sensor) to be powered by the thermoelectric generator.

Electronic components typically have a maximum rated temperature up to which the electronic components may operate on a nominal basis. Approaching the maximum rated temperature of the electronic components may result in a reduction in the performance of the electronic components. Exceeding the maximum rated temperature of the electronic components may result in damage or failure of the electronic components. A failure of the electronic components may compromise the capability of the thermoelectric generator to power the device.

A thermoelectric generator may be installed in an environment where the temperature of the heat source fluctuates. For example, the thermoelectric generator may be thermally coupled to the surface of a heated pipe in an industrial facility. Process variations may result in fluctuations in the surface temperature of the heated pipe such that heat flow to the thermoelectric generator may fall outside of the range for maximum operating efficiency of the thermoelectric generator. Heat flow from the heated pipe may also result in exceeding the maximum rated temperature of the electronic components that may be coupled to the thermoelectric generator.

As can be seen, there exists a need in the art for a system and method for adjusting heat flow from a heat source such that the thermoelectric generator may operate at maximum efficiency and is thermally protected from overheating. In addition, there exists a need in the art for a system and method for adjusting heat flow from a heat source such that electronic components are maintained below their maximum rated temperature and are therefore thermally protected from overheating, and also such that the electronic components may operate at maximum efficiency.

SUMMARY

The above-described needs associated with adjusting heat flow from a heat source are specifically addressed and alleviated by the present disclosure which, in an embodiment, provides a variable-thermal-resistance mounting system. The variable-thermal-resistance mounting system may include a cylinder coupled to a heat source or a heat load. The heat source may have an optimal warm-side temperature. The variable-thermal-resistance mounting system also may include a rod movably engaged to the cylinder. The rod may be coupled to the remaining one of the heat source or heat load. The rod may be axially slidable relative to the cylinder between a collapsed position and an extended position in a manner causing a change in heat flow between the heat source and the heat load in a manner such that the warm-side temperature of the heat load is set at a substantially optimal value.

In a further embodiment, disclosed is a variable-thermal-resistance mounting system including a cylinder and a rod movably engaged to the cylinder. A heat source may be mounted to an end of the cylinder. The rod may be coupled to a thermoelectric generator which may be mounted on an end of the rod. The thermoelectric generator may have an optimal warm-side temperature. The rod may be axially slidable relative to the cylinder between a collapsed position and an extended position in a manner causing a change in thermal resistance between the heat source and the thermoelectric generator in a manner such that the warm-side temperature of the thermoelectric generator is initially set at a substantially optimal value.

Also disclosed is a method of regulating heat flow between a heat source and a heat load. The method may include coupling a rod to one of a heat source and a heat load, and coupling a cylinder to a remaining one of the heat source and the heat load. The method may additionally include axially moving the rod relative to the cylinder between a collapsed position and an extended position. Furthermore, the method may include changing a heat flow between the heat source and the heat load in response to moving the rod between the collapsed position and the extended position, and adjusting a warm-side temperature of the heat load in response to changing the heat flow.

The features, functions and advantages that have been discussed can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings below.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the present disclosure will become more apparent upon reference to the drawings wherein like numbers refer to like parts throughout and wherein:

FIG. 1A is a schematic diagram of a heat source coupled to a thermal device (e.g., a heat load mounted on a thermal platform) via a variable-thermal-resistance mounting system comprising a rod engaged to a cylinder and which is shown in a collapsed position;

FIG. 1B is a schematic cross-sectional diagram of the variable-thermal-resistance mounting system in an extended position;

FIG. 1C is a schematic cross-sectional diagram of a cross sectional view of a mechanical clamp locking the axial position of the rod relative the cylinder;

FIG. 2 is a schematic cross-sectional diagram of the variable-thermal-resistance mounting system wherein the heat load is configured as a thermoelectric generator;

FIG. 3A is a schematic cross-sectional diagram of an embodiment of the variable-thermal-resistance mounting system wherein the cylinder contains a cylinder fluid that expands and contracts when respectively heated and cooled;

FIG. 3B is a schematic cross-sectional diagram of the variable-thermal-resistance mounting system of FIG. 3A wherein the mounting system is in an extended position;

FIG. 4A is a schematic cross-sectional diagram of an embodiment of the variable-thermal-resistance mounting system having a bellows containing a bellows fluid;

FIG. 4B is a schematic cross-sectional diagram of the variable-thermal-resistance mounting system of FIG. 4A in an extended position as a result of expansion of the bellows fluid;

FIG. 5A is a schematic cross-sectional diagram of an embodiment of the variable-thermal-resistance mounting system wherein the bellows is thermally isolated from a thermally low-conductive shaft that is axially slidable within a shaft guide mounted in the cylinder;

FIG. 5B is a schematic cross-sectional diagram of the embodiment of the variable-thermal-resistance mounting system of FIG. 5A in an extended position as a result of expansion of the bellows fluid;

FIG. 6A is a schematic cross-sectional diagram of an embodiment of the variable-thermal-resistance mounting system wherein the cylinder and the rod have a vernier-type structure;

FIG. 6B is a schematic cross-sectional diagram of the embodiment of the variable-thermal-resistance mounting system of FIG. 6A in an extended position as a result of expansion of the bellows fluid;

FIG. 7A is a schematic cross-sectional diagram of an embodiment of the variable-thermal-resistance mounting system wherein the vernier-type structure of the cylinder and the rod have a linear configuration and showing the rod in a collapsed position;

FIG. 7B is a schematic cross-sectional diagram of the embodiment of the variable-thermal-resistance mounting system of FIG. 7A showing the rod in an extended position;

FIG. 7C is a schematic cross-sectional diagram of an embodiment of the vernier-type structure having a non-linear configuration and showing the rod in a collapsed position;

FIG. 7D is a schematic cross-sectional diagram of an embodiment of the vernier-type structure having a non-linear configuration and showing the rod in an extended position;

FIG. 8 is a schematic cross-sectional diagram of an embodiment of the variable-thermal-resistance mounting system having a chimney for drawing cool air into the chimney for convective cooling of a heat load mounted within the chimney such as a thermoelectric generator and/or an electronics enclosure;

FIG. 9A is a schematic cross-sectional diagram of an embodiment of the variable-thermal-resistance mounting system having a motor for actively controlling the extension of the rod relative to the cylinder;

FIG. 9B is a schematic cross-sectional diagram of the embodiment of the variable-thermal-resistance mounting system of FIG. 9A showing the rod in an extended position;

FIG. 10 is a schematic cross-sectional diagram of an embodiment of the variable-thermal-resistance mounting system having a thermal divider positioned between the thermal device (e.g., a heat load) and the heat source;

FIG. 11 is a schematic cross-sectional diagram of an embodiment of the variable-thermal-resistance mounting system having the thermal divider positioned between a thermoelectric generator and the heat source;

FIG. 12 is a flow chart illustrating one or more operations that may be included in a method of regulating heat flow between a heat source and a heat load; and

FIG. 13 is a schematic diagram of a thermal path from a heat source to a heat load and wherein the thermal path includes the variable (e.g., adjustable) thermal resistance of the presently-disclosed variable-thermal-resistance mounting system and the thermal resistance of a thermal load such as a thermoelectric generator.

DETAILED DESCRIPTION

Referring now to the drawings wherein the showings are for purposes of illustrating various embodiments of the present disclosure, shown in FIG. 1A is a schematic illustration of a heat source 100 thermally coupled to a heat load 106 (e.g., a thermal device 102) by means of a manually-adjustable variable-thermal-resistance mounting system 130. A heat load 106, such as for example, a thermoelectric generator 110, has a heat capacity and possesses structural elements to collect heat energy from the heat source 100, as well as dissipate all or a portion of the collected heat energy. Advantageously, the variable-thermal-resistance mounting system 130 provides a means for adjusting or regulating (e.g., optimizing) heat flow from the heat source 100 to a thermal device 102 or heat load 106. The heat source 100 may comprise a structure having a surface temperature than is higher than the ambient temperature. In a non-limiting embodiment, the heat source 100 may comprise a heated pipe having a surface temperature that is higher than ambient temperature of the surrounding environment. However, the heat source 100 may comprise any type of system, subsystem, assembly, or structure from which heat may flow from the heat source 100 to the heat load 106 or thermal device 102.

The thermal device 102 or heat load 106 may comprise any type of device having a desired or predetermined warm-side temperature 114 or warm-side temperature range. The heat load 106 may also have a maximum temperature such as a maximum operating temperature. For example, the thermal device 102 may include one or more temperature-sensitive components 108 such as a sensor, an imaging device, or any device having a maximum rated operating temperature. In an embodiment, the thermal device 102 may be a thermoelectric generator 110. The thermoelectric generator 110 may have an optimal temperature range within which the thermoelectric generator operates at maximum efficiency. For example, the thermoelectric generator 110 may have an optimal warm-side temperature 114 similar to the T_(Warm) temperture of the thermal load (designated by R_(Load)) in the schematic diagram of FIG. 13 and described below.

The thermoelectric generator 110 may be coupled to electronic components 112 such as conditioning electronics for conditioning the voltage produced by the thermoelectric generator 110 prior to delivery to a device (e.g., a sensor) to be powered by the thermoelectric generator 110. The efficiency of the conditioning electronics may be at a maximum at an optimal voltage generated by the thermoelectric generator 110. Due to the dependency of the thermoelectric voltage on the temperature gradient across the thermoelectric generator 110, the generated voltage may change if the temperature of the heat source 100 changes resulting in reduced conversion efficiency. In this regard, initially setting or maintaining a substantially constant optimal temperature on one side (e.g., the warm-side temperature 114) of the thermoelectric generator 110 may ensure maximum operating efficiency of the conditioning electronics (e.g., electronic components 112) for conditioning the voltage produced by the thermoelectric generator 110.

Advantageously, any one of the presently-disclosed embodiments of the variable-thermal-resistance mounting system 130 operates to adjust heat flow from a heat source 100 such that the thermoelectric generator 110 may operate at maximum efficiency by maintaining the warm-side temperature 114 at a substantially constant value or within a temperature range. In addition, the variable-thermal-resistance mounting system 130 may adjust heat flow in a manner such that the thermal load is thermally protected from overheating. In addition, the variable-thermal-resistance mounting system 130 operates to adjust heat flow from a heat source 100 such that electronic components 112 are maintained below their maximum rated temperature and are therefore thermally protected from overheating, and may operate at maximum efficiency.

Referring briefly to FIG. 13, shown is a schematic diagram of a thermal path for heat flow from a heat source to a heat load. The thermal path includes a series of thermal resistances arranged in series and including the variable (e.g., adjustable) thermal resistance of the presently-disclosed variable-thermal-resistance mounting system and the thermal resistance of a thermal load such as a thermoelectric generator. In FIG. 13, T_(Source) may be described as the surface temperature of the heat source. Thermal resistance of the heat source is neglected in the diagram. T_(Sink) may be described as the temperature of the ambient environment. T_(Warm) may be described as the warm-side temperature of the thermal load such as a warm-side temperature of a thermoelectric generator. ΔT_(Var) may be described as the temperature gradient across the variable-thermal-resistance mounting system. ΔT_(Load) may be described as the temperature gradient across the thermal load (e.g., across the thermoelectric generator). ΔT_(Ext) may be described as the external temperature gradient. R_(Var) may be described as the variable thermal resistance of variable-thermal-resistance mounting system (e.g., the cylinder-rod configuration and mechanical mount with adjustable thermal interface—see FIGS. 1A-6B and 8-11). R_(Load) may be described as the thermal resistance of the thermal load which may be a thermoelectric generator or other device. In the case where the thermal load is a thermoelectric generator, the thermoelectric generator may be described as a system containing a series of thermal resistances such as of a heat collector (e.g., thermal platform), the thermoelectric generator itself, and a heat exchanger (e.g., a heat sink such as ambient environment).

Refering to FIG. 13, the variable-thermal-resistance mounting system allows for maintaining T_(Warm) at a substantially constant (e.g., optimal) temperature. In addition, the variable-thermal-resistance mounting system may prevent T_(Warm) from exceeding a maximum rated temperuare which may otherwise result in overheating of the thermoelectric generator. If T_(Source) increases, then the variable-thermal-resistance mounting system may be manually, passively, and/or actively adjusted to increase R_(Var), in a manner as described below, such that T_(Warm) is maintained at a substantially constant (e.g., optimal) temperature. If T_(Source) decreases, then the variable-thermal-resistance mounting system may be manually, passively, and/or actively adjusted to reduce R_(Var), in a manner as described below, such that T_(Warm) is maintained at the substantially constant (e.g., optimal) temperature

The thermal device 102 may include a thermal platform 104. The thermal platform 104 may provide a stable mechanical support for coupling the heat load 106 (e.g., thermoelectric generator) to the thermal interface 134 comprising a rod 140 slidably coupled to a cylinder 136 as described below. In addition, the thermal platform 104 may have a larger cross-sectional area than the rod 140 to distribute the heat from the rod and spread out the heat across the cross sectional area of the heat load 106 and thereby avoid temperature concentrations in localized areas of the heat load 106. In an embodiment, the thermal platform 104 may be comprised of one or more layers of materials each having individual predetermined thermal conductivity values and selected geometries (e.g., cross-sectional geometry and thicknesses). The thermal conductivity values and the geometry (e.g., thicknesses) of the one or more layers of the thermal platform 104 may be selected to provide a desired temperature range for the thermal device 102 or heat load 106. In this manner, selection of the materials for the thermal platform 104 may provide a means for tuning the system to provide a desired amount of heat to the thermal device 102 (e.g., heat load 106) within an optimum temperature range. For example, the thermal platform 104 may include one more metallic or non-metallic layers such as at least one layer of aluminum having a relatively high thermal conductivity of approximately 230 Watts/meter-Kelvin as a high end of range. On the opposite end of the thermal conductivity spectrum, the thermal platform 104 may include at least one layer of polytetrafluoroethylene (Teflon™) having a relatively low thermal conductivity of approximately 0.25 Watts/meter-Kelvin which is approximately 100 times lower than the thermal conductivity of aluminum. The thermal platform 104 may include other layers of material to provide a relatively narrow working range for the warm-side temperature of the heat load 106. In some embodiments, the thermal platform 104 may be comprised of two metallic layers having an insulting layer sandwiched therebetween. The metallic layers may provide mechanical stability to the connection of the heat load 160 to the rod 140. The thermal platform 104 may assist in spreading the heat from the rod 140 and thereby provide substantially uniform heat flow into the cross-sectional area of the thermal device 102 or heat load 106. The heat load 106 may be coupled to the thermal platform 104 using mechanical fasteners and/or adhesive or other means.

In an embodiment, the thermal device 102 may comprise an energy harvesting system such as a thermoelectric generator 110 as illustrated in FIG. 2 and described below. The thermoelectric generator 110 may receive heat flow from the heat source 100 for providing a temperature gradient across the thermoelectric generator 110 such that the thermoelectric generator 110 may generate a voltage. The thermal platform 104 may be configured to mechanically couple the thermoelectric generator 110 to the variable-thermal-resistance mounting system 130 disclosed herein. In addition, the thermal platform 104 may allow for substantially uniform heat distribution into the thermoelectric generator 110 and provide a relatively narrow working range for the warm-side temperature 114 of the thermoelectric generator 110. In addition, the thermal platform 104 may integrate several layers each having a different thermal conductivity in order to tailor the thermal resistance of the thermal platform 104. In this regard, the materials of the thermal platform 104 may be selected to provide a desired level of thermal resistance between the heat source 100 and the cylinder 136 to achieve a relatively narrow working range for the warm-side temperature 114. In some embodiment, the materials of the thermal platform 104 may be selected considering the working fluid 194 in the bellows (FIG. 4A-6B) as discussed below wherein a relatively high temperature may be required to expand the bellow fluids 194.

As indicated above, the variable-thermal-resistance mounting system 130 may include a thermal interface 134 comprising a rod 140 that may be slidably coupled to a generally hollow cylinder 136. The cylinder 136 may be mechanically coupled at one end to the heat source 100 via a mechanical mount 132. The mechanical mount 132 may be fastened to the cylinder 136 such as by using mechanical fasteners. The torque of the mechanical thrusters may influence the heat transfer capability between the heat source 100 and the mechanical mount 132. The mechanical mount 132 may include an arrangement of one or more materials that may be selected in consideration of the temperature range of the heat source 100 such that a desired temperature range is provided at the location where the cylinder 136 is mechanically coupled to the mechanical mount 132. In this regard, the materials of the mechanical mount 132 may be selected to provide a desired level of thermal resistance between the heat source 100 and the cylinder 136 similar to that which is described above with regard to the thermal platform 104. A heat shield 158 may be provided between the thermal device 102 and the heat source 100 to minimize radiative heat transfer to the thermal device 102. The heat shield 158 may be formed of relatively thin-gauge metal or non-metallic material and may be provided in a size that is larger (e.g., wider) than the thermal device 102 (e.g. heat load 106) and/or other components (e.g., temperature-sensitive electronics) that may be mounted adjacent to the heat load 106.

In FIG. 1A, the rod 140 may have a cross sectional shape that is complementary to the cross sectional shape of the interior of the cylinder 136. For example, the rod 140 may have a rod outer surface 142 sized and configured to provide a sliding fit with the interior surface of the cylinder 136. The overlap in contact between the rod outer surface 142 and the cylinder inner surface 138 may define a contact surface area 144 between the rod 140 and cylinder 136. The amount of contact surface area 144 may correspond to the axial position of the rod 140 relative to the cylinder. The rod 140 and the cylinder 136 may be provided in any cross-sectional shape, without limitation and are not limited to a cylindrical shape. In some embodiments, the rod 140 and the cylinder 136 may be sized and configured to provide an annular gap between the rod 140 and the cylinder 136 as shown in FIGS. 3A-3B as described below.

In certain embodiments (e.g., FIGS. 1A-1B), the mounting system 130 may include a mechanical clamp 146 that may be sized and configured complementary to the rod 140. The rod 140 may extend out of the end of the cylinder 136 opposite the heat source 100. The thermal device 102 may be coupled to the rod end. The thermal resistance of the mounting system 130 may be adjusted by adjusting the amount by which the rod 140 is axially pushed or extended out of the cylinder 136 to thereby adjust the amount of contact surface area 144 between the rod 140 and the cylinder 136. In any of the embodiments disclosed herein, the rod 140 may be axially moved relative to the cylinder 136 to any position between and including a collapsed position 152 and an extended position 154. FIG. 1A illustrates the thermal interface 134 of the rod 140 and cylinder 136 in the collapsed position 152 providing a minimum or reduced amount of thermal resistance to heat flow from the heat source 100 to the heat load 106. In the collapsed position 152, a maximum portion of the rod 140 may be axially positioned within the cylinder 136 to provide an increased contact surface area 144 for increased heat flow from the heat source 100 to the thermal device 102 (e.g., the heat load 106).

FIG. 1B illustrates the thermal interface 134 of the rod 140 and cylinder 136 in one of a variety of different extended position 154 at which the rod 140 may be positioned relative to the cylinder 136. The rod 140 may be axially displaced to an extended position 154 to at least initially set the warm-side temperature 114 of the heat load 106. In some passive or active embodiments described below, the system 130 may adjust the warm-side temperature to a substantially constant value or to be maintained within a temperature range. In an extended position 154, the thermal interface 134 of the rod 140 and cylinder 136 may provide a reduced amount of thermal resistance to the heat flow from the heat source 100 to the heat load 106 relative to the thermal resistance provided by the rod 140 and cylinder 136 in the collapsed position 152. In the extended position 154, a relatively larger portion of the rod 140 is axially extended outside of the cylinder 136 to provide a relatively small amount of contact surface area 144 between the rod 140 and the cylinder 136. A small amount of contact surface area 144 may minimize or reduce the amount of heat flow passing from the cylinder 136 into the rod 140 and into the thermal device 102. In some embodiments, the axial position of the rod 140 relative to the cylinder 136 may be manually adjusted to provide any level of heat resistance. The amount of rod 140 extension and the amount of contact surface area 144 between the rod 140 and cylinder 136 may be defined based on the extension length 156 as shown in FIG. 1B. In this regard, the axial position of the rod 140 relative to the cylinder 136 may be adjusted to a desired extension length 156 to regulate the heat flow from the cylinder 136 into the rod 140 and thereby maintain the thermal device 102 (e.g., heat load 106) at a desired warm-side temperature 114 or within a desired temperature range.

FIG. 1C is a sectional illustration of the cylinder 136 and rod 140 taken along line 1C of FIG. 1B and illustrating a mechanical clamp 146 that may be included with the variable-thermal-resistance mounting system 130. In an embodiment, the mechanical clamp 146 may be mounted to the cylinder 136 such as on an end of the cylinder 136 or in any other suitable location. The mechanical clamp 146 may facilitate the coupling or locking of the axial position of the rod 140 relative to the cylinder 136. In one example, the mechanical clamp 146 may include a set screw ring 148 that may be coupled to the end of the silver. The set screw ring 148 may have an inner diameter that may be complementary to the rod 140 outer diameter. The set screw ring 148 may include a set screw 150 for engaging or locking the rod 140 to the cylinder 136 to prevent relative movement therebetween. The set screw 150 may be engaged after adjusting the axial position of the rod 140 relative to the cylinder 136.

FIG. 2 illustrates an embodiment of the variable-thermal-resistance mounting system 130 configured similar to the system illustrated in FIGS. 1A-1C except in FIG. 2, the thermal load may be a thermoelectric generator 110. An electronics enclosure 112 may be mounted adjacent to the thermoelectric generator 110. The electronics enclosure 112 may contain electronics for power management or power conditioning for the thermoelectric generator 110. In an embodiment not shown, the electronics may be contained or integrated within the thermoelectric generator 110.

FIGS. 3A-3B illustrate an embodiment of a passively-adjusted variable-thermal-resistance mounting system 130 wherein the cylinder 136 contains a cylinder fluid 172 that expands and contracts when respectively heated and cooled. The fluid may comprise a gas, a liquid, or a two-phase gas/liquid composition that alternates between gas and liquid depending upon the temperature. The rod 140 may be a hollow rod 170 to provide increased volume within the cylinder 136 for the cylinder fluid 172. A seal 174 may be included at the end of the cylinder 136 to provide a seal 174 between the rod outer surface 142 and the cylinder inner surface 138 to prevent the cylinder fluid 172 from escaping from the cylinder 136.

In FIG. 3A, the cylinder fluid 172 may be trapped or contained within the volume of the cylinder 136 such that an increase in temperature of the cylinder fluid 172 due to heat from the heat source 100 and resulting in an increase in cylinder fluid pressure 176 within the cylinder 136. The increase in cylinder fluid pressure 176 may push or extend the rod 140 out of the cylinder 136 (see FIG. 3B) thereby increasing the extension length 156 between the thermal platform 104/heat load 106 and the end of the cylinder 136. The increase in extension length 156 corresponds to a reduced length of the rod 140 within the cylinder 136. The reduced length of the rod 140 within the cylinder 136 corresponds to a reduction in the heat flow transfer from the cylinder 136 wall into the cylinder fluid 172 and into the rod 140 and thereby resulting in an increase in thermal resistance between the heat source 100 to heat load 106. The increase in thermal resistance may reduce heat flow and thereby protect the heat load 106 and related components from over-temperature.

In some embodiments, the variable-thermal-resistance mounting system 130 may operate in a manner such that a relatively small increase in heat source 100 temperature will result in a relatively small increase in the cylinder fluid 172 temperature causing a correspondingly small extension length 156 of the rod 140 out of the cylinder 136 and a relatively small increase in thermal resistance to heat flow from the heat source 100 to the heat load 106. Conversely, a relatively large increase in the heat source 100 temperature may result in a relatively large increase in the cylinder fluid 172 temperature causing a correspondingly large extension length 156 of the rod 140 out of the cylinder 136 and a relatively large increase in thermal resistance to heat flow from the heat source 100 to the heat load 106.

As shown in FIG. 3B, in an embodiment, the variable-thermal-resistance mounting system 130 may include an extension spring 178 (e.g., a tension spring) which may be mounted between the rod 140 and the heat source 100. In an embodiment, the extension spring 178 may be configured to bias the rod 140 from an extended position 154 (FIG. 3B) back toward a collapsed position 152 (FIG. 3A). In this manner, the extension spring 178 may allow the variable-thermal-resistance mounting system 130 to operate in a passive manner to maintain the warm-side temperature 114 at a substantially constant value or within a temperature range. In addition, the extension spring 178 may provide a means for tuning the thermal resistance of the system. For example, the extension spring 178 may be preloaded when the rod 140 is in a fully retracted position. The preloading of the extension spring 178 may provide a means for controlling (e.g., increasing) the temperature at which the rod 140 starts to axially displace or extend out of the cylinder 136.

FIGS. 4A-4B illustrate a further embodiment of a passively-adjusted variable-thermal-resistance mounting system 130 having a bellows 192 or a bladder filled with bellows fluid 194. The bellows fluid 194 may comprise a gas, a liquid, or a two-phase gas/liquid combination. The bellows 192 may be mechanically coupled to the rod 140 and the cylinder 136 and may be located between the thermal device 102 and the cylinder 136 end. In an embodiment, the rod 140 may be configured as a relatively highly-thermally conductive rod 140. Heat from the heat source 100 may be conducted along the rod 140 and into the bellows fluid 194. The bellows fluid 194 may expand from heat from the heat source 100 causing the bellows 192 to increase in length and resulting in an increase in the extension length 156 (e.g., axial displacement) of the rod 140 from the retracted position (FIG. 4A) to an extended position 154 (FIG. 4B). In this manner, the bellows 192 in FIGS. 4A-4B may provide indirect control of the thermal resistance.

As indicated above, an increase in the extension length 156 of the rod 140 may result in a reduction in the heat resistance of the thermal interface 134 between the rod 140 and the cylinder 136. A reduction in heat resistance may result in a decrease in heat flow from the heat source 100 to the thermal device 102 and may protect heat load 106 components from over-temperature. The bellows fluid 194 may contract when cooled which may result in the bellows 192 decreasing in length and the rod 140 retracting into the cylinder 136 as shown in FIG. 4A and which may decrease the heat resistance between the rod 140 and the cylinder 136 resulting in an increase in heat flow from the heat source 100 to the thermal device 102. The expansion and contraction of the bellows fluid 194 may provide a means to passively maintain the warm-side temperature 114 of the heat load 106 (e.g., thermoelectric generator) at a substantially constant value or within a temperature range. Although not shown, a retraction spring may be included to retract the bellows 192 toward the collapsed position 152 and causing the rod to retract into the cylinder 136. The bellows 192 may also be constructed of material having a memory (e.g., stainless steel) which, when the temperature drops, may act as a return mechanism for biasing the rod 140 from an extended position 154 toward the collapsed position 152.

Advantageously, in an embodiment, the bellows 192 may also provide structural support to the thermal device 102 on an exterior of the cylinder 136. In this regard, the bellows 192 may mechanically stabilize the connection between the thermal device 102 and the cylinder 136. The bellows material, the bellows geometry, and the bellows fluid 194 may also provide for a wide range of adjustability for altering the thermal resistance of the variable-thermal-resistance mounting system 130. The bellows fluid 194 may be provided as a liquid that boils at a predetermined temperature to increase the bellows fluid pressure 196 and cause displacement of the rod 140. Alternatively, the bellows fluid 194 may comprise an inert gas. The mechanical mount 132, the rod 140, the cylinder 136, the bellows fluid 194, and the thermal platform 104 may be selected to provide a relatively narrow working temperature range at the heat load 106.

Although not shown, the bellows 192 may be replaced with a bi-metallic spring/lever for axially displacing or extending the rod 140 out of the cylinder 136. In an embodiment, the bi-metallic spring may be comprised of two components (e.g., two different metals) fastened together and having different coefficients of thermal expansion. Heat flow from the heat source 100 may be thermally transferred along the cylinder 136 and/or rod 140 and into the bi-metallic spring result in mechanical displacement (e.g., curvature) of the bi-metallic spring due to the differences in coefficients of thermal expansion and causing the heat load 106 to be moved the axially away from the heat source 100 and thereby increasing the thermal resistance to heat flow from the heat source 100 to the head load.

FIGS. 5A-5B illustrate a further embodiment of the variable-thermal-resistance mounting system 130 configured in a manner similar to the embodiment of FIGS. 4A-4B and wherein the bellows 192 may provide for direct control of the thermal resistance. In the embodiment shown in FIGS. 5A-5B, the bellows 192 may be directly coupled to the cylinder 136 end and the heat load 106 or thermal device 102. In addition, the bellows 192 may be thermally isolated from a thermally low-conductive shaft 190 that may be slidable within a shaft guide 198 mounted within the cylinder 136. In an embodiment, the shaft guide 198 may be formed of material having a relatively low thermal conductivity to minimize heat flow from the cylinder 136 into the rod 140. Heat from the heat source 100 may flow along the cylinder 136 walls and into the bellows fluid 194. The heating of the bellows fluid 194 may cause axial displacement of the rod 140 from a retracted position (FIG. 5A) to any one of a variety of different extended positions 154 (FIG. 5B) as described above. In any embodiment, the bellows fluid 194 may have a composition that becomes less thermally conductive with an increase in the temperature of the bellows fluid 194. In this manner, the system may provide a non-linear change in thermal resistance in response to increases in temperature at the heat source 100.

FIGS. 6A-6B illustrate an embodiment of the variable-thermal-resistance mounting system 130 configured similar to the embodiment of FIGS. 5A-5B and wherein the cylinder 136 and the rod 140 have a vernier-type structure 212. In this regard, the cylinder 136 and/or the rod 140 may each include one or more axially-spaced, segmented thermal contacts 210. The segmented thermal contacts 210 may provide a further means for tailoring the rate of change of the thermal resistance of the system with changes in the temperature of the heat source 100. For example, the cylinder 136 and the rod 140 in FIGS. 6A-6B are shown as each having two sets of segmented thermal contacts 210 positioned along the cylinder 136 between the cylinder 136 and the rod 140. The thermal contacts 210 may have defined thermal resistances. The thermal contacts 210 in FIGS. 6A-6B are of unequal length which may result in a non-linear change in heat resistance with changes in extension length 156 of the rod 140 relative to the cylinder 136. Advantageously, the vernier-type structure 212 disclosed herein may provide a means for significantly changing the thermal resistance of the mounting system with minimal displacements (e.g., several millimeters) of the rod 140.

FIGS. 7A-7B illustrate an embodiment of the variable-thermal-resistance mounting system 130 with the vernier-type structure 212 of the rod 140 and cylinder 136 having a linear configuration 216. In this regard, the rod 140 and the cylinder 136 may each include axially-spaced thermal contacts 210 that may be substantially equal in length. The segmented thermal contacts 210 of the rod 140 may be sized to provide a sliding fit with the segmented thermal contacts 210 of the cylinder 136. The thermal contacts 210 in any embodiment disclosed herein may preferably have a relatively high surface hardness to minimize wear of the thermal contacts 210 during sliding movement. In an embodiment, the thermal contacts 210 may be formed of nickel-plated copper, aluminum, steel, or other material. The thermal contacts 210 may optionally be provided with an oxidized or anodized surface. The substantially equal lengths of the axially-spaced thermal contacts 210 may result in a linear decrease in the contact surface area 144 between the thermal contacts 210 when the rod 140 is axially displaced relative to the cylinder 136. In this manner, the substantially equal lengths of the axially-spaced thermal contacts 210 may result in a linear change in thermal resistance upon axial displacement of the rod 140.

FIGS. 7C-7D illustrate an embodiment of the variable-thermal-resistance mounting system 130 with the vernier-type structure 212 having a non-linear configuration 214. In this regard, the axially-spaced thermal contacts 210 for each one of the rod 140 and the cylinder 136 may be of unequal lengths. The unequal lengths of the axially-spaced thermal contacts 210 may result in a non-linear decrease in contact surface area 144 between the thermal contacts 210 when the rod 140 is axially displaced relative to the cylinder 136. In this manner, the unequal lengths of the thermal contacts 210 may provide a non-linear change in thermal resistance between the heat source 100 and the heat load 106.

In FIGS. 7A-7D, the vernier-type structure 212 arrangement for the rod 140 and the cylinder 136 may advantageously provides a means for adjusting the thermal resistance of the system independent of axial displacement of the rod 140 relative to the cylinder 136. In this regard, the total contact surface area between the thermal contacts 210 at any given axial position of the rod 140 relative to the cylinder 136 may be determined by the quantity of thermal contacts 210, the geometry at the interface between the thermal contacts 210, the thermal contact length, the thermal contact width, and the thickness of the thermal contacts 210. In addition, the relative thermal resistance at a given axial displacement of the rod 140 may be determined by a combination of the thermal contact sizes, shapes, and configurations, the material of the thermal contacts 210, and other parameters which may collectively provide a wide range of capability for adjusting the thermal resistance of the system 130.

FIG. 8 illustrates an embodiment of a variable-thermal-resistance mounting system 130 that may include a chimney 230 arrangement for convective cooling of a heat load, 106, an electronics enclosure 112, a thermoelectric generator 110, or any thermal device 102 that may be included with a heat load 106 or which may be thermally coupled to the heat load 106 or located adjacent to the heat load 106. In FIG. 8, the chimney 230 may be applied to any of the above-described mounting system 130 embodiments. The heat shield 158 may be configured to form a shaft or chimney 230 having an open bottom end 232 and an open top end 234. The heating of the thermal device 102 (e.g., the thermoelectric generator 110) may cause cool air 236 to be drawn into the bottom end of the chimney 230. The cool air 236 may pass over the electronics enclosure 112 and/or the thermoelectric generator 110 for convective cooling thereof. The air may exit out of the top end of the chimney 230.

FIGS. 9A-9B illustrates an embodiment of an actively-controlled variable-thermal-resistance mounting system 130 and which may include a motor 160 for controlling the extension or axial displacement of the rod 140 relative to the cylinder 136. In an embodiment, the motor 160 may comprise a direct current (DC) motor 160 although any type of motor may be used. The motor 160 may be powered by a thermoelectric generator 110 although the motor 160 may be powered by other means such as a battery. The motor 160 may be coupled to a drive mechanism such as a screw drive mechanism 162. The motor 160 may receive a signal from the thermal device 102 (e.g., heat load 106) such as when the heat load 106 reaches a predetermined temperature. For example, a signal may be provided to the motor 160 when the heat load 106 reaches an upper limit temperature or when the warm-side temperature 114 or range is exceeded causing activation of the motor 160 to axially extend the rod 140 further out of the cylinder 136 from a retracted position (FIG. 9A) toward an extended position 154 (FIG. 9B). In this manner, the motor 160 may move the heat load 106 away from the heat source 100 and thereby decrease heat flow into the heat load 106. In some embodiments, when the heat load 106 reaches a low temperature limit such as when the warm-side temperature 114 falls below a predetermined value or range, a signal may activate the motor 160 to retract the rod 140 into the cylinder 136 to move the heat load 106 toward the heat source 100. In this manner, the motor 160 may actively control the displacement of the rod 140 relative to the cylinder 136 to adjust the thermal resistance therebetween and thereby control heat flow from the heat source 100 to the heat load 106.

FIGS. 10-11 illustrate embodiments of a variable-thermal-resistance mounting system 130 having a thermal divider 250 positioned between the thermal device 102 (e.g., heat load 106) and the heat source 100. In FIG. 11, the thermal device 102 may be configured as a thermoelectric generator 110 which may have a separate electronics enclosure 112 or which may integrate the electronics components within the thermoelectric generator 110. The thermal divider 250 may be included in applications where the heat source 100 operates at a relatively high upper temperature. The embodiment may further include a heat shield 158 as described above and located between the heat load 106 and the thermal divider 250 to further minimize radiative heating of the thermal device 102. Advantageously, the thermal divider 250 may include radiator fins 252 for rejecting heat to the ambient environment. In this manner, the thermal device 102 (e.g., thermoelectric generator 110) may be protected from relatively high heat flow. The ratio of heat flow through the radiator to heat flow through the heat load 106 may be adjustable by adjusting the displacement of the rod 140.

In some embodiments disclosed herein, the arrangement of the rod 140 and cylinder 136 may be configured such that the rod 140 is connected to the heat source 100 and the cylinder 136 is connected to the thermal device 102 (e.g., heat load 106, thermoelectric generator 110, etc.). For example, in contrast to the embodiment of FIGS. 1A-1B, the rod 140 may be fixedly coupled on one end to the heat source 100, and the cylinder 136 may be fixedly coupled on an opposite end to the thermal device 102. The cylinder 136 may be displaced relative to the rod 140 by any one of the above-described embodiments including by manual means, passive means (e.g., with a fluid-filled cylinder or fluid-filled bellow), or active means (e.g., with a motor).

Although each of the embodiments is described as having a single rod 140 sliding within a single cylinder 136, the mounting system may be provided with two or more rods 140 arranged in parallel and sliding within two or more cylinders 136. In any one of the above described embodiments, a temperature-indicating device such as a strip may be provided on an exterior of the cylinder 136 or the thermal device 102 to provide an indication of the temperature of the system. For example, a liquid crystal strip may be mounted on an exterior of the thermal platform 104 of the heat load 106 or on an exterior of a thermoelectric generator 110. The strip may change color corresponding to changes in temperature and may provide a visual indication to an observer as to whether the thermal platform 104 is in the desired temperature range.

Referring to FIG. 12, shown is a flow chart illustrating one or more operations that may be included in a method 300 of regulating heat flow between a heat source 100 and a heat load 106 such as a thermoelectric generator 110. Step 302 of the method 300 may include coupling a rod 140 to a heat source 100 or a heat load 106, and coupling a cylinder 136 to the remaining heat source 100 or the heat load 106. For example, as illustrated in FIGS. 1A-6 and 8-11, the heat source 100 may be coupled to an end of the cylinder 136 and the heat load 106 may be coupled to an end of the rod 140. However, the variable-thermal-resistance mounting system 130 may be configured with the heat source 100 may be coupled to an end of the rod 140 and the heat load 106 coupled to an end of the cylinder 136. In some embodiments, the heat source 100 may be coupled to the rod 140 or the cylinder 136 using a mechanical mount 132 formed of material providing a desired level of thermal resistance between the heat source 100 and the cylinder 136 or rod 140. The heat load 106 may be coupled to the rod 140 or the cylinder 136 using a thermal platform 104 comprised of one or more materials or layers of material each having predetermined thermal conductivity value as discussed above, and/or a selected geometry (e.g., cross-sectional geometries and/or thicknesses) selected in consideration of a desired operating temperature range of the heat load 106 or the electronics.

Step 304 of the method 300 may include axially moving the rod 140 relative to the cylinder 136 between a collapsed position 152 and an extended position 154 as shown in FIGS. 1A-1B. For example, the heat load 106 may be manually pulled away from the heat source 100 which may result in the rod 140 being extended at least partially out of the cylinder 136. The rod 140 may be axially moved to any position between the collapsed position 152 and the extended position 154. Extending the rod 140 at least partially out of the cylinder 136 may result in changing (e.g., decreasing) the contact surface area 144 between the rod 140 and cylinder 136.

Step 306 of the method 300 may include changing a heat flow between the heat source 100 and the heat load 106 in response to moving the rod 140 between the collapsed position 152 and the extended position 154. For example, when the rod 140 is extended out of the cylinder 136, the change (e.g., decrease) in contact surface area 144 may result in altering (e.g., decreasing) heat flow between the heat source 100 and the heat load 106 as a means to at least initially set or adjust the warm-side temperature 114 of the heat load 106. In some embodiments, the method 300 may optionally include mounting a heat shield 158 (FIGS. 1A-1B) and/or a thermal divider 250 (FIG. 10) between the heat load 106 and the heat source 100 as shown in FIGS. 1A, 1B, and 2, for reducing radiative heat transfer to the heat load 106.

Step 308 of the method 300 may include adjusting the warm-side temperature 114 of the heat load 106 in response to changing the heat flow. In some examples, the warm-side temperature 114 may be initially adjusted to a substantially optimal value which, in the present disclosure, may be described as within a relatively small range of the optimal value. In some embodiments, the warm-side temperature 114 may be initially adjusted by manually pulling the rod 140 out of the cylinder 136 to a position that initially results in substantially achieving the optimal warm-side temperature 140 or relatively small range based on a given temperature of the heat source 100. If the heat source temperature changes, then further adjustment of the position of the rod 140 may be required to accordingly adjust the warm-side temperature 114. In an embodiment, the method may include clamping or fixing the position of the rod 140 relative to the cylinder 136 after the warm-side temperature 114 has been adjusted. For example, the rod 140 may be clamped to the cylinder 136 such as by using a mechanical clamp 146, an embodiment of which is shown in FIG. 1C described above.

In some embodiments, the variable-thermal-resistance mounting system 130 may be operated in a passive manner without manually or actively displacing (e.g., manually or actively pulling) the rod 140 axially outwardly from the cylinder 136 or manually or actively (e.g., with a motor—FIGS. 9A-9B) pushing the rod 140 inwardly back into the cylinder 136. For example, certain passive embodiments of the variable-thermal-resistance mounting system 130 may include a cylinder 136 containing a cylinder fluid 172 such as a gas, a liquid, or a 2-phase fluid as shown in FIGS. 3A-3B and described above. In such embodiments, the method 300 may further include heating the cylinder fluid 172 with heat from the heat source 100, and expanding the cylinder fluid 172 when heated causing an increase in cylinder fluid pressure 176 within the cylinder 136. The increase in cylinder fluid pressure 176 may cause the rod 140 to at least partially extend out of the cylinder 136, resulting in an increase in thermal resistance between the rod 140 and cylinder 136. The increase in thermal resistance may result in a reduction in heat flow between the heat source 100 and the heat load 106.

The method 300 of varying the thermal resistance between a heat load 106 and a heat source 100 may also be implemented in a passive manner using a variable-thermal-resistance mounting system 130 having a bellows 192 containing a bellows fluid 194. The bellows 192 may be mounted between the heat load 106 and the cylinder 136 as shown in FIGS. 3A-7D. In such an embodiment, the method 300 may include heating the bellows fluid 194 with the heat flow from the heat source 100, expanding the bellows fluid 194 when heated causing the bellows 192 to increase in length, and extending the rod 140 out of the cylinder 136 due to the increasing length of the bellows 192. The method 300 may further include increasing the thermal resistance between the rod 140 and the cylinder 136 due to the extension of the rod 140, and reducing the heat flow between the heat source 100 and the heat load 106 as a result of the increase in the thermal resistance.

In some embodiments, the bellows 192 may be thermally isolated from the rod 140 in a manner such that the heat flow from the heat source 100 may be conducted along the cylinder 136 and directly into the bellows fluid 194 as shown in FIGS. 4A-6B and described above. In other embodiments, the cylinder 136 and the rod 140 may each include at least two axially-spaced segmented thermal contacts 210 forming a vernier-type structure 212. The thermal contacts 210 of the rod 140 may be slidably engaged to the thermal contacts 210 of the cylinder 136. The vernier-type structure 212 may have a linear configuration 216 with substantially equal length thermal contacts 210 for each of the rod 140 and cylinder 136 as shown in FIGS. 7A-7B. For a linear configuration 216, the method 300 of varying the thermal resistance between the heat source 100 and heat load 106 may include axially moving the rod 140, and linearly changing the thermal resistance of the cylinder 136 and rod 140 in response to axially moving the rod 140. For a non-linear configuration 216 214 of the vernier-type structure 212 wherein each one of the rod 140 and cylinder 136 has unequal length thermal contacts 210 as shown in FIGS. 7C-7D, axially moving the rod 140 relative to the cylinder 136 may result in linearly changing the thermal resistance of the cylinder 136 and rod 140.

In some embodiments, the variable-thermal-resistance mounting system 130 may be actively operated to vary the thermal resistance between the heat source 100 and heat load 106. For example, in the embodiment shown in FIGS. 9A-9B having a motor 160 operatively coupled to the rod 140, the method 300 may include actively displacing or axially moving the rod 140 relative to the cylinder 136. For example, the method 300 may include using a motor 160 (e.g., a D.C. motor) coupled to the rod 140 with a screw drive mechanism 162 to actively axially displace the rod 140 relative to the cylinder 136. In some embodiments, the method may include powering the motor 160 using the thermoelectric generator 110 which may be the heat load 106 for which the temperature is being regulated using the variable-thermal-resistance mounting system 130. In other embodiments, the motor 160 may be powered using one or more batteries or another power source.

In some embodiments, the method 300 may include mounting the heat load 106 within a chimney 230 as shown in FIG. 8. The chimney 230 may be formed using one or more heat shields 158. In addition to axially displacing the rod 140 to control the heat flow from the heat source 100 into the heat load 106, the chimney 230 may further facilitate controlling the temperature of the heat load 106. For example, the method 300 may include drawing cool air 236 into the open bottom end 232 of the chimney 230, passing the cool air 236 over a heat load such as a thermoelectric generator 110 and/or electronics enclosure 112 to convectively cool the thermoelectric generator 110 and/or electronics enclosure 112, and discharging the air out of a top end of the chimney 230.

Additional modifications and improvements of the present disclosure may be apparent to those of ordinary skill in the art. Thus, the particular combination of parts described and illustrated herein is intended to represent only certain embodiments of the present disclosure and is not intended to serve as limitations of alternative embodiments or devices within the spirit and scope of the disclosure. 

What is claimed is:
 1. A variable-thermal-resistance mounting system, comprising: a cylinder coupled to one of a heat source and a heat load, the heat load having an optimal warm-side temperature; a rod movably engaged to the cylinder and being coupled to a remaining one of the heat source and heat load; and the rod being axially slidable relative to the cylinder between a collapsed position and an extended position in a manner causing a change in heat flow between the heat source and the heat load such that the warm-side temperature of the heat load is initially set at a substantially optimal value.
 2. The system of claim 1, wherein: the rod extending out of the cylinder by an extension length when the rod is in an extended position; the cylinder has a cylinder inner surface; the rod having a rod outer surface in contact with the cylinder inner surface along a contact surface area; and the contact surface area increasing and decreasing in correspondence with a respective increase and decrease in the extension length.
 3. The system of claim 1, wherein: the heat load comprises a thermoelectric generator.
 4. The system of claim 1, further comprising: a mechanical clamp configured to axially lock an axial position of the rod relative to the cylinder.
 5. The system of claim 1, further comprising: a mechanical mount coupling the heat source to the rod or the cylinder and being formed of material providing a desired level of thermal resistance between the heat source and the cylinder or rod.
 6. The system of claim 1, further comprising: a thermal platform coupling the heat load to the rod or the cylinder; and the thermal platform being formed of one or more thermal materials having a predetermined thermal conductivity and geometry selected to provide a desired operating temperature range of the heat load.
 7. The system of claim 1, wherein: the cylinder contains a cylinder fluid that expands when heated causing an increase in pressure within the cylinder; and the increasing cylinder pressure extending the rod out of the cylinder causing an increase in a thermal resistance between the rod and cylinder and a reduction in the heat flow between the heat source and the heat load.
 8. The system of claim 1, further comprising: a bellows located between the heat load and the cylinder, the bellows containing a bellows fluid that expands when heated causing the bellows to increase in length; and the increase in bellows length causing extension of the rod and a reduction in heat flow between the heat source and the heat load.
 9. The system of claim 8, wherein: the bellows fluid contracts upon cooling causing the bellows to decrease in length; and the decrease in bellows length resulting in retraction of the rod and an increase in heat flow between the heat source and the heat load.
 10. The system of claim 1, wherein: the cylinder and the rod each include at least two segmented contacts in axially slidable engagement with one another; and the segmented contacts being sized and configured such that axial movement of the rod causes a change in thermal resistance of the cylinder and rod.
 11. The system of claim 10, wherein: the cylinder and rod each have at least two segmented contacts axially spaced from one another and of substantially equal length such that axial movement of the rod causes a linear change in thermal resistance of the cylinder and rod.
 12. The system of claim 10, wherein: the cylinder and rod each have at least two segmented contacts axially spaced from one another and of unequal length such that axial movement of the rod causes a non-linear change in thermal resistance of the cylinder and rod.
 13. The system of claim 1, wherein: a motor coupled to the rod and actively controlling axial displacement of the rod relative to the cylinder for adjusting a thermal resistance between the rod and the cylinder.
 14. A variable-thermal-resistance mounting system, comprising: a cylinder coupled to a heat source; a rod movably engaged to the cylinder and being coupled to a thermoelectric generator having an optimal warm-side temperature; and the rod being axially slidable relative to the cylinder between a collapsed position and an extended position in a manner causing a change in thermal resistance between the heat source and the thermoelectric generator such that the warm-side temperature of the thermoelectric generator is initially set at a substantially optimal value.
 15. A method of regulating heat flow between a heat source and a heat load, comprising the steps of: coupling a rod to one of a heat source and a heat load, and coupling a cylinder to a remaining one of the heat source and the heat load; axially moving the rod relative to the cylinder between a collapsed position and an extended position; changing a heat flow between the heat source and the heat load in response to moving the rod between the collapsed position and the extended position; and adjusting a warm-side temperature of the heat load in response to changing the heat flow.
 16. The method of claim 15, wherein the cylinder has a cylinder inner surface, the rod has a rod outer surface slidably engaged to the cylinder inner surface along a contact surface area, the method further comprising: extending the rod out of the cylinder; changing the contact surface area in correspondence with extending the rod; and altering the heat flow between the heat source and heat load in response to changing the contact surface area.
 17. The method of claim 15, wherein the cylinder contains a cylinder fluid, the method further comprising: heating the cylinder fluid with heat from the heat source; expanding the cylinder fluid when heated causing an increase in pressure within the cylinder; extending the rod out of the cylinder in response to the increasing cylinder pressure; increasing a thermal resistance between the rod and cylinder in response to pushing the rod; and reducing the heat flow between the heat source and the heat load in response to increasing the thermal resistance.
 18. The method of claim 15, wherein a bellows is mounted between the heat load and the cylinder, the bellows containing a bellows fluid, the method further comprising: heating the bellows fluid with heat from the heat source; expanding the bellows fluid when heated causing the bellows to increase in length; extending the rod at least partially out of the cylinder in response to increasing a bellows length; increasing a thermal resistance between the rod and cylinder in response to extending the rod; and reducing the heat flow between the heat source and the heat load in response to increasing the thermal resistance.
 19. The method of claim 18, further comprising: allowing the bellows fluid to cool; contracting the bellows fluid upon cooling resulting in the bellows decreasing in length; retracting the rod at least partially into the cylinder in response to decreasing the bellows length; decreasing a thermal resistance in response to retracting the rod; and increasing the heat flow between the heat source and the heat load in response to decreasing the thermal resistance.
 20. The method of claim 15, wherein the cylinder and the rod each include at least two axially-spaced segmented contacts of substantially equal length and in axially slidable engagement with one another, the method further comprising; axially moving the rod relative to the cylinder; and linearly changing a thermal resistance of the cylinder and rod in response to axially moving the rod.
 21. The method of claim 15, wherein the cylinder and the rod each include at least two axially-spaced segmented contacts of unequal length and in axially slidable engagement with one another, the method further comprising; axially moving the rod relative to the cylinder; and non-linearly changing a thermal resistance of the cylinder and rod in response to axially moving the rod. 